1. Field of the Invention
The present invention relates to a transfer car that can lift and lower a vehicle body and can turn the vehicle body around a vertical axis, that is, has a lifting and lowering function and a turning function, and an automobile assembly line using the transfer car having a lifting and lowering function and a turning function.
2. Description of the Background Art
Vehicle bodies are generally transferred in a state where the vehicle bodies are hung by an overhead conveyor in a chassis process for mounting a chassis and an engine on a vehicle body in an automobile assembly line of a fitting factory and between the respective processes in the line (for example, see patent document 1).
Moreover, in the automobile assembly line, the vehicle bodies are generally transferred in a state where the vehicle bodies are placed on a transfer car conveyor in a trim process for mounting interior parts on the vehicle body and in a final process for mounting exterior parts on the vehicle body, and in these processes are used transfer cars that can lift and lower the vehicle body to a height suitable for the operation of mounting the parts, that is, has a lifting and lowering function (for example, see patent document 2).
Here, in these processes have been also used transfer cars that has a steering mechanism for steering wheels, which are mounted on a lower portion of the base of a transfer car having a lifting and lowering function in such a way as to be steered and can be rolled on a travel road, and that additionally has a turning function for changing the orientation of the vehicle body, in other words, transfer cars that has a lifting and lowering function and a turning function (for example, see patent document 2).    Patent document 1: Japanese Unexamined Utility Model Publication No. Sho 57-123315 (FIGS. 1 and 2)    Patent document 2: Japanese Unexamined Patent Publication No. Sho 62-168769 (FIGS. 1 to 4)
In the overhead conveyor hung from the building as described in the patent document 1, travel rails need to be installed above the heads of operators (for example, near the ceiling of the factory) and a high-elevation operation using heavy equipment are required to install the travel rails. Thus, extra caution must be taken for safety and a large number of man-hours are required to install auxiliary beams, hangers, safety nets, inspection corridors and ladders, and the like in the field. In addition, to hang the overhead conveyor and auxiliary equipment from the building, the building is required to have strength meeting a hung load and hence the construction cost of the building is increased so as to increase the strength of the building.
Moreover, the transfer car having a lifting and lowering function as described in the patent document 2 does not present the problem of increasing the installation cost of the overhead conveyor and the construction cost as described in the patent document 1, but a pair of right and left guide posts erected on the base are near the vehicle body and hence interfere with the operation of mounting parts on the under floor of the vehicle body.
Further, the transfer car having a turning function as described in the patent document 2 is constructed in such a way that the wheels mounted on the lower side of the transfer car are steered by the steering mechanism driven with an air cylinder to thereby turn the entire transfer car. Thus, the vehicle body (transfer car) cannot be turned when the front and rear transfer cars are not separated from the transfer car by a specified distance or more (for example, the vehicle body cannot be turned in a state where the front and rear transfer cars are adjacent to the transfer car), nor the vehicle body can be relatively turned with respect to the operator so as to facilitate the operation of the operator operating on the base or to eliminate the useless operation of the operator.
Still further, the transfer car traveling on a transfer path is mounted with air cylinders of actuators for the steering mechanism for steering the respective wheels, so that these air cylinders need to be supplied with air from the outside of the transfer car.
Still further, in the conventional automobile assembly line, the vehicle bodies in the chassis process for mounting parts on the under floor of the vehicle body are transferred by the overhead conveyor, and the vehicle bodies in the trim process for mounting interior parts on the vehicle body and in the final process for mounting exterior parts on the vehicle body are transferred in a state where the vehicle bodies are placed on a transfer car conveyor. In this manner, the overhead conveyor and the transfer car conveyor are mixedly installed, so that as described above, the installation of the overhead conveyor increases installation cost and construction cost and the guide posts for the transfer cars having a lifting and lowering function interfere with the operation of mounting parts on the under floor of the vehicle body.
Still further, as described above, even when the transfer cars additionally provided with the turning function are used, there is a limit to turning the vehicle body, which cannot always improve workability and reduces the degree of flexibility of the automobile assembly line to be constructed by the use of the transfer cars.
In addition, there is no commonality of transfer equipment and the overhead conveyor and the transfer car conveyor are mixedly installed, which increases the number of necessary transfer units. This increases cost by that much and decreases availability and increases the number of vehicle bodies in process.
Thus, what the present invention is going to solve in view of the above-mentioned circumstances is to provide a transfer car that has a lifting and lowering function and a turning function and that has high workability and a high degree of flexibility in constructing a line, and an automobile assembly line that uses the transfer car having a lifting and lowering function and a turning function and that can reduce cost, shorten a construction time, increase availability, and reduce the number of vehicle bodies in process.